The present invention relates to a fuel injection pump and, more particularly, to a sintered cam ring for a fuel injection pump. Furthermore, the present invention pertains particularly to a sintered cam ring for a fuel injection pump which has a rotor rotating therein and is secured at the outer portion thereof to a body by means of a bolt.
Examples of the fuel injection pump having a cam ring in which a rotor rotates inside the body thereof include "Distributor Type Fuel Injection Pump" (Japanese Patent Laid-Open No. 35,260/1983) laid open on Mar. 1, 1983. As the sintered cam ring used as the cam ring for a fuel injection pump, an example has been introduced in which a through hole and a screw are provided on a sintered cam ring from the outer periphery to the inner periphery thereof after the cam ring has been subjected to annealing, the example being shown in FIG. 3 and mentioned in the description taken in conjunction therewith in a paper under the title "Production of Full-Density M2 Automotive Diesel Parts via the HTM TM Powder Metal Process", collected in "SAE Technical Paper Series 800,309", proposed by John A. Rassenfoss at the 75th anniversary of the Society of Automotive Engineers, Inc. held at the Congress and Exposition Cobo Hall in Detroit, U.S.A. from 25 to 29 of February, 1980.
The thus constructed sintered cam ring is positioned and secured to the body thereof in such a manner that the sintered cam ring is subjected to thread cutting in the radial direction thereof and is secured to the body in a lateral direction. Such positioning and securing of the sintered cam ring encounters the following disadvantages:
In sintering a cam ring with a preparatory hole opened therein, the sintering temperature exceeds 1,200.degree. C., so that the sintered cam ring reaches a high degree of hardness. Therefore, a thread for screwing a bolt for securing the sintered cam ring to the body cannot be cut in the preparatory hole of the sintered cam ring unless this high degree of hardness is properly lowered. For this reason, it is conventional practice to conduct thread cutting after carrying out annealing and then to effect quenching above 1,200.degree. C. in order to obtain a necessary strength.
Thus, the conventional sintered cam ring inconveniently requires carrying out annealing for cutting a thread in the preparatory hole, as well as quenching and tempering after sintering the cam ring, and therefore disadvantageously needs a large number of steps in positioning and securing the sintered cam ring to the body thereof.